Process of bating skins in leather manufacture



Patented on. 4,1938 v 2,132,366 I UNITED STATES PATENT OFFICE PROCESS OF BATING SKINS IN LEATHE MANUFACTURE John Arthur Wilson, Milwaukee, Wis., assignor,

by mesne assignments, to Monsanto Chemical Company, a corporation of Delaware No Drawing. Application May 10, 1935,

Serial No. 20,770

Claims. (Cl. 195-6) This invention relates to tanning processes and fering properties not possessed by the loose mixmaterials, and has for its object certain improvetures of the constituent salts.

'- ments in the bating operation as. applied to the While generally I may employ any alkali metal treatment of hides and skins in the manufacture dehydrated polyphosphate, I prefer to use the 5 ofleather. sodium salts because of their relative cheapness 5 The action of the known digestive enzymes in and commercial availability. the bating process has for its object the attack The hating liquor is made to contain from 1 to' and disintegration of some fraction of the hide grams per liter of, say, sodium polyphosphate or skin and the removal of specific structures havingapH in 1% solution of 7.10. The quantity 10 which affect the appearance of the grained surof the phosphate employed may be varied over a 10 face of the finished leather. considerable range, which will be dependent upon Eatin s ca d on just prior to the tanning the alkali present in the hides. The bating bath operation, and is effected by means of a panis prepared by making asolution of the phosphate creatic enzyme which is most effective at a pH described above, immersing the hides theren, and v value of 7.4. The skins contain lime when enterby means of acid additions adjusting the pH to 15 ing the bate liquor, and the diffusion of the 7.4, which is the optimum hydrogen ion concenlime into the liquor makes it alkaline. A method I tration for the action of the digestive enzyme. now in use to keep the pH value at 1.4 is to add' The pancreatic enzyme is then added to the bath sulfuric acid to the liquor during the entire peand hating continued over a period of, say, 60

' go riod of bating, regulating the flow of acid accordminutes. ing to measurements of the pH value every 2 or I have carried out a series of comparable bating 3 minutes. experiments which illustrate the use of my im- The necessity for such frequent measurements proved process. Acontrol test in which no phosof pH makes control diflicult and introduces an phate was employed required the continuous adelement of danger if the work is not done with dition of acid over the period of the test. 26

great accuracy. When 1 gram per liter of either the sodium I have now found that certain alkali metal polyphosphate described above or tetra sodium polyphosphates, also referred to herein as molecupyrophosphate was used, only occasional small larly dehydrated alkali metal phosphates, may" additions of acid were required, the pyrophosso be used in the bate bath with great advantage as phate requiring slightly more than the metaphos- 80 to the product obtained and remarkable simphate. plicity in the control of the hating operation When 5 grams per liter of either phosphate were itself. present in the bate bath, no further additions of Those phosphates which I have found to be of acid were required.

value in my process comprise the water-soluble When no phosphate was used in hating, the 35 forms of the alkali metal.- metaphosphates. or calcium oxide content of the hated stock on the alkali metal pyrophosphates, or mixtures of the dry basis was 1.31%; with 1 gram per liter of two in varying proportion. Loose mixtures of sodium polyphosphate, it was 1.14%; with 5 these two classes of phosphates may be used, pargrams, 1.13%; and with 10 grams, it was 0.59%.

40 ticularly when employing the acid pyrophos- With 1 gram of pyrophosphate it was 1.25%; with 40 phate; but where ease in handling these prod- 5 grams. a d W th 10 gram-S, it was 0.69%- ucts isa consideration I may employ f s d I have described above certain results obtained tures of meta and tetrapyrophosphates. These m the batmg operation using Sodium P1YPh5r phate having a pH in 1% water solution of 7.10. products may be made by mixing together vary Such product is commercially available at present,

45 ing proportions of mono-alkali metal and (ii-alkali metal orthophosphates, heating the mixture to the z i w i g i gg g g figi figggg igg ggg gg fusion 9" and quickly cooling the Same See 20% tetra sodium pyrophosphate. Because of the British Patent 378,345 of 1932' Such treat method of manufacture, which involves a fusion of the mixtures of meta and Pyrophosphates of the constituent salts or their equivalents fol- 50 results in the formation of soluble polyphosphates lowed by quickly cooling the same, the pyrophoswhich are new compounds, a chemical combinaphate has lost its chemical identity, having betion having occurred between the constituents come merged t t metaphosphate t t of such mixtures, and it has been found that the ent, forming the new polyphosphate. Varying water-soluble fused mixtures have enhanced bufproportions of the two constituents may, of 55 course, be employed to form the new molecularly dehydrated polyphosphates and the resultant hydrogen ion eflect considerably modified. The range of hydrogen ion concentrations which may be obtained may be varied from the lower value of about 6.3 for sodium metaphosphate to an upper value of 10.6 for tetra sodium pyrophosphate. The product as produced commercially may contain small amounts of sodium orthophosphate and also acid sodium pyrophosphate present as impurities.

In many cases I may employ boric acid in conjunction with the phosphates herein mentioned. I have found that the amount of sulfuric acid required to neutralize the lime in the hides varies from 2 to 20 pounds per pack of skins. This is due to variations in the lime content. For convenience in application, I find it desirable to prepare three diiferent grades of bates, as follows:

For stock of low lime content I prefer to employ a mixture of 88% boric acid, 10% sodium acid pyrophosphate, and 2% concentrated enzyme. Approximately 1.5 pounds of this mixture is employed per 1000 pounds of stock.

For stock of medium lime content I prefer to use a mixture of 94% boric acid, 5% sodium acid pyrophosphate, and 1% concentrated enzyme. Approximately 3 pounds of this mixture is employed per 1000 pounds of stock.

For stock of high lime content I prefer to use a mixture of 97% boric acid, 2.5% sodium acid pyrophosphate, and 1% concentrated enzyme. Approximately 6 pounds of this mixture would be employed per 1000 pounds of stock.

While I have described above certain specific forms of my invention, it will be appreciated that it is susceptible to various changes and modifications without departing from the spirit thereof, and I desire, therefore, that it be not limited except as indicated by the prior art or as "particularly pointed out in the claims.

What I claim is:

1. A process for bating hides including treating said hides with a solution comprising a pancreatic digestive enzyme having hide bating properties, and a water soluble alkaline compound of sodium meta phosphate and tetra sodium pyrophosphate.

2. A process for bating hides including treating said hides with a solution comprising a pancreatic digestive enzyme having hide bating properties and a water soluble compound of sodium meta phosphate and tetra sodium pyrophosphate, said compound having a pH value greater than 7.0.

3. A process for bating hides including treating said hides with a solution comprising a pancreatic digestive enzyme having hide bating properties and a water soluble compound of sodium meta phosphate and sodium pyro'phosphate, said solution being maintained during bating at a pH in the neighborhood of 7.4.

4. A process for bating hides, including treating said hides with a solution comprising a pancreatic digestive enz e and a water soluble alkali metal polyphos hate. I

5. A process for hating hides comprising treating said hides in water with a pancreatic digestive enzyme and a water soluble sodium polyphosphate.

JOHN ARTHUR WILSON. 

